The present invention relates to a floating bush bearing.
A floating bush bearing comprises a stationary bush, a rotary shaft and a floating bush rotatably fitted therebetween and is intended to improve the bearing capacity so that heat produced may be minimized and vibration may be prevented. FIG. 1 is a cross sectional view of a prior art floating bush bearing. A rotary shaft 2 which is driven by a prime mover is supported through a rotatable floating bush 3 in a stationary bush 1 securely fitted into a frame or the like. The cylindrical wall of the floating bush 3 is formed with a plurality of oil holes and the inner wall surface of the floating bush 3 is formed with a circular groove in communication with these oil holes. When a lubricating oil is fed into the space between the stationary and floating bushes 1 and 3, it is distributed through the oil holes and the circular oil groove over the whole inner wall surface of the floating bush 3 so that oil films 4 and 5 are formed over the outer and inner wall surfaces of the floating bush 3, respectively.
Upon rotation of the rotary shaft 2, it floats because of the oil film 5 formed over the inner wall surface of the floating bush 3 and the floating bush 3 is drawn by the inner oil film 5 and is therefore rotated. In this case, the floating bush 3 floats and rotates between the outer and inner oil films 4 and 5 so that it is well lubricated and less heat is produced. That is, the heat produced due to the viscosity of the oil films is in proportion to the square of a relative sliding speed if the oil films have the same thickness. Therefore, if a floating bush bearing instead of a conventional bearing having only one oil film is used and the floating bush 3 rotates at a speed one half (1/2) of that of the rotary shaft, the heat produced from each of the two oil films 4 and 5 of the floating bush 3 becomes 1/4 of the heat produced in the conventional bearing. Even if the calorific values of the oil films 4 and 5 are summed, the overall heat produced is ony 1/2 of the heat produced in the conventional bearing.
As described above, if the floating bush 3 rotates at a speed one half (1/2) of that of the rotary shaft 2, the calorific value becomes 1/2 as compared with the conventional bearing, so that the bearing performance is improved. However, in practice, as many literatures report, the floating bush 3 is difficult to be rotated and hardly rotates especially when the rotary shaft 2 starts rotating. The reason why it is difficult to cause the rotation of the floating bush 3 is as follows:
That is, upon rotation of the rotary shaft 2, the inner oil film 5 is formed and the floating bush 3 is drawn by the inner oil film 5 and tends to rotate. The force for causing the rotation of the floating bush 3 is a dynamic frictional force, while a static frictional force which is far greater than the dynamic frictional force is produced between the floating bush 3 and the stationary bush 1 prior to the formation of the outer oil film 4. As described above, the performance of the conventional floating bush bearing is not so satisfactory that it has not been widely used in practice.
Japanese Patent Publication No. 48-15536 discloses an intermediate gear device which is substantially similar in construction to the floating bush bearing. FIG. 2 is a longitudinal sectional view thereof. A driving 7 and an output shaft 8 are supported by frames 6 in coaxial relationship. A planet gear shaft 10 is supported in parallel with the driving and output shafts 7 and 8 by a supporting frame 9 integral with the output shaft 8. A planet gear 12 which is in mesh with a driving gear 11 integral with the driving shaft 7 is carried through an auxiliary gear 13 by the planet gear shaft 10. The auxiliary gear 13 is also in mesh with the driving gear 11. Reference numerals 14 and 15 denote an internal gear and a spacer, respectively. A plurality of the planet gear shafts 10, the planet gears 12, the auxiliary gears 13 and the spacers 15 are equiangularly disposed.
When the driving shaft 7 is rotated, the planet gears 12 rotate themselves, while revolving around the driving gear 11 so that the output shaft 8 is rotated in unison with the supporting frame 9. When the intermediate gear device of the type described is compared with the floating bush bearing as shown in FIG. 1, it is seen that the planet gear shaft 10, which is not rotated, corresponds to the stationary bush 1 and that the auxiliary gear 13 which is fitted over the planet gear shaft 10 corresponds to the floating bush 3. In addition, the planet gear 12, which is in mesh with the auxiliary gear 13 and rotates, corresponds to the rotary shaft 2. Therefore, from the standpoint of construction and in view of the fact that a lubricating oil is supplied to the gears in mesh with each other, the intermediate gear device of the type described above may be regarded as a floating bush bearing. In the intermediate gear device, as the auxiliary gear 13 is in mesh with the driving gear 11 and is rotated at the same speed as the planet gear 12, the auxiliary gear 13 functions as the floating bush 3, as described above. As a result, less heat is produced and machining errors can be absorbed. Furthermore, because the oil films serve to prevent vibration, the load can be equally distributed among the planet gears 12.
However, in the intermediate gear device of the type described above, the force for causing the rotation of the auxiliary gear 13 is too small so that the static deflections of the teeth of the aux11iary gear 13 become considerably less than machining errors. As a result, when one tooth leaves from another tooth and engages with the next tooth, vibrations are caused so that the tooth surfaces are worn out and broken.